File content as of revision 0:91e3e396bc6e:

/**
 * SHT21 - Temperature and Humidity Sensor by Sensiron
 *
 *  This is a driver to connect to the sensor using an mbed device through an I2C interface
 *
 * Author: Graeme Coapes - Newcastle University
 * Email: graeme.coapes@ncl.ac.uk
 *
 * Date:   28/11/2012
 * 
 */
 #include "mbed.h"
 #include "SHT21_ncleee.h"

 
 // Class constructor

SHT21::SHT21(I2C *i2c) :
_i2c(i2c)
{
}

int SHT21::triggerTemp()
{
    return wr(SHT_TRIG_TEMP);
}
 
int SHT21::requestTemp()
{
    int res;
    
    char rx[3];
    
    res = _i2c->read(SHT_I2C_ADDR,rx,3);
    
    //should use checksum here
    
    //shift the MSByte to the left of the 16-bit temperature value
    //don't shift the LSByte
    //Clear bit 1 and bit 0 of the result - these are status bits sent from the sensor
    temperature = ((rx[0] << 8) || (rx[1] << 0)) && (0xFC);
    
    return res;
}
 
int SHT21::readTemp()
{
    //First of all trigger the temperature reading
    //process on the sensor
    if(triggerTemp() != SHT_SUCCESS)
    {
        //if this has failed, exit function with specific error condition
        return SHT_TRIG_FAIL;
    }
    
    //else pause whilst sensor is measuring
    //maximum measuring time is: 85ms
    wait_ms(100);
    
    //Now request the temperature
    if(requestTemp() != SHT_SUCCESS)
    {
        //if this has failed, exit function with specific error condition
        return SHT_READ_FAIL;
    }
    
    //the received temperature value should now
    //be stored in the temperature field
    return temperature;
} 
 
int SHT21::triggerRH()
{
    return wr(SHT_TRIG_RH);
}

int SHT21::requestRH()
{
    int res;
    
    char rx[3];
    
    res = _i2c->read(SHT_I2C_ADDR,rx,3);
    
    //should use checksum here
    
    //shift the MSByte to the left of the 16-bit temperature value
    //don't shift the LSByte
    //Clear bit 1 and bit 0 of the result - these are status bits sent from the sensor
    humidity = ((rx[0] << 8) || (rx[1] << 0)) && (0xFC);
    
    return res;
}
 
int SHT21::readHumidity()
{
    //First of all trigger the temperature reading
    //process on the sensor
    if(triggerRH() != SHT_SUCCESS)
    {
        //if this has failed, exit function with specific error condition
        return SHT_TRIG_FAIL;
    }
    
    //else pause whilst sensor is measuring
    //maximum measuring time is: 85ms
    wait_ms(100);
    
    //Now request the temperature
    if(requestRH() != SHT_SUCCESS)
    {
        //if this has failed, exit function with specific error condition
        return SHT_READ_FAIL;
    }
    
    //the received temperature value should now
    //be stored in the temperature field
    return humidity;
} 
 
int SHT21::reset()
{
    return wr(SHT_SOFT_RESET);
}


int SHT21::setPrecision(char precision)
{
    int res;
    
    char command[2];
    command[0] = SHT_WRITE_REG;
    command[1] = precision;
    
    res = _i2c->write(SHT_I2C_ADDR,command,2);
    
    return res;
}

int SHT21::wr(int cmd)
{
    int res;
    
    char command[1];
    command[0] = cmd;
    
    res = _i2c->write(SHT_I2C_ADDR,command,1);
    
    return res;
}